1. Field of the Invention
The present invention relates to a piezoelectric vibrator used in an acoustic transducing electronic appliance (such as an enclosure vibration type flat speaker or receiver) or in a vibration transducing electronic appliance such as a vibrator. More particularly, the invention relates to a piezoelectric vibrator having improvements in shock resistance, mountability, and reliability.
2. Description of the Related Art
Piezoelectric vibrators utilizing piezoelectric elements are widely employed as simple electro-acoustic transducers and actuators. Especially, in recent years, they are often used in the field of mobile phones, personal digital assistants, and so on. A conventional piezoelectric vibrator (e.g., Japanese Patent Laid-open No. 2000-224696-, especially FIGS. 4-8)) uses a bimorph device or unimorph device obtained by bonding together piezoelectric elements on the surface of a metallic vibrating plate. The device is supported around its center by a support member, constituting a cantilevered piezoelectric vibrator. When this vibrator is driven, high driving force is obtained in a low frequency range.
In another actuator, plural piezoelectric vibrating plates having different resonant frequencies are used to produce a distribution mode. For example, International Publication WO 01/54450, especially FIG. 9, discloses a transducer in which plural rectangular_piezoelectric vibrating plates are supported as a piezoelectric vibrator for a panel speaker by a single pillar substantially parallel over the panel. Vibration of the piezoelectric vibrating plates is transmitted to the panel via the pillar to thereby vibrate the panel. Thus, sound is produced. Japanese Patent Laid-open No. 2000-134682, especially FIGS. 1 and 3, describes a sound-producing device in which one or more disk-like piezoelectric vibrating plates are supported by a single pillar. A resilient body is mounted along the fringes of the vibrating plates. Thus, the acoustic feature is improved.
FIG. 10 shows one example of the conventional piezoelectric vibrators. In the shown piezoelectric vibrator 200, a piezoelectric vibrating body 201 is fixed on an acoustic panel 202, a body 201 consisting of a pillar 204 and piezoelectric vibrating plates 206, 212. The piezoelectric vibrating plates 206 and 212 are supported by the pillar 204 so as to be substantially parallel to the acoustic panel 202. The piezoelectric vibrating plate 206 is considered to have a bimorph structure. That is, piezoelectric elements 209 and 210 are bonded to a vibrating plate 208 made of a metal-based material such as 42 alloy or a resinous material such as polyethylene terephthalate (PET). An electrode layer of Ni, Pd, Ag, or the like is formed on a surface of each of the piezoelectric elements 209 and 210. The other piezoelectric vibrating plate 212 is similar in structure. Piezoelectric elements 215 and 216 are bonded to a vibrating plate 214. Thus, a bimorph structure is formed. The pillar 204 is molded from a metal-based material such as stainless steel or from a resinous material such as PET or acrylonitrile butadiene styrene (ABS). The acoustic panel 202 is made of glass or aluminum of honeycomb structure, for example.
Lead wires 222 and 228 are connected to the electrodes of the piezoelectric vibrating plates 206 and 212 and the vibrating plates 208, 214 by a conductive paste or by solder 218, 220, 224, 226, for example. An electrical signal is applied via the lead wires 222 and 228, so that the piezoelectric vibrating plates 206 and 212 vibrate. The vibration is transmitted to the pillar 204. The vibration is further transmitted via the pillar 204 to the acoustic panel 202 to which the piezoelectric vibrating body 201 is fixed. Consequently, the acoustic panel 202 vibrates, producing sound. However, the conventional device described so far has the following problems.
(1) When an impact load is applied to the piezoelectric vibrating body, an excessive stress is applied to the piezoelectric vibrating plates. This may destroy the piezoelectric elements made of a fragile material, or they may come off the pillar or the vibrating plates may bend. In this way, structural damage occurs. In addition, a pyroelectric effect produces an electromotive force. Concomitantly with this, there arises the danger that the circuit is affected. Furthermore, where plural piezoelectric vibrating plates are used, contact between any piezoelectric vibrating plate and its enclosure leads to destruction of the piezoelectric elements. Further, collision between the piezoelectric vibrating plates destroys the piezoelectric elements.
(2) Where plural piezoelectric vibrating plates are used, mounting methods including an electrical connection method such as soldering using cotton threads, bonding of the piezoeletric vibrating plates to the pillar, and mounting of the pillar and electrical connector terminals are complicated. This deteriorates the productivity and increases the cost of production.